The present invention is directed to bicycle control devices and, more particularly, to a fluid pressure apparatus for a bicycle.
Some bicycle control devices operate using pressure from a fluid such as air, water, oil, etc. One example of such a device is shown in German Offenlegungsschrift No. 195 14 267. The device disclosed in that document comprises a fluid pressure cylinder, a piston that is axially slidably disposed within the cylinder, a pair of rods that extend from opposite sides of the piston, an actuating member that presses against one of the rods, and a bushing that guides the other rod. First and second fluid ports are located on opposite sides of the piston so that fluid flows through the first fluid port when the actuating member moves the piston in one axial direction, and fluid flows through the second fluid port when the actuating member moves the piston in the opposite direction. As a result, two operations of a control device coupled to the first and second fluid ports can be performed using a single piston and fluid pressure cylinder.
The fluid in the pressure cylinder normally acts as a biasing mechanism, similar to a pair of springs mounted on opposite sides of the piston, that maintains the piston in a desired home position between the first and second fluid ports. However, if the fluid pressure on opposite sides of the piston is unbalanced, then the piston will be located in the improper position relative to the first and second fluid ports. As a result, the actuating member will have to be moved asymmetrically, thereby creating discomfort for the rider.